Studies are being carried out to determine whether the cyclic nucleotides may mediate the effects of prolactin on the metabolism of mammary glands from mice. Levels of cyclic AMP and cyclic GMP will be measured in tissues treated with prolactin and in mammary tissues taken from mice during pregnancy and lactation. Further studies will be carried out to determine if prolactin affects the activities of the enzymes which catalyze the synthesis and degradation of the cyclic nucleotides. An attempt will also be made to obtain a prolactin effect on epithelial cells obtained from collagenase digested mammary tissues. Experiments will also be carried out to determine whether the prostaglandins may be intracellular mediators for the actions of prolactin on the mammary gland. Attempts will be made to 1) mimic or suppress the actions of prolactin on RNA and casein synthesis with the prostaglandins and 2) to measure whether prolactin affects the level of prostaglandins in the mammary gland.